1. Field of the Invention
The present invention relates to a semiconductor device controlling an electrostatic actuator using MEMS (Micro Electro Mechanical Systems) and a method of controlling an electrostatic actuator.
2. Description of the Related Art
Recently, MEMS has attracted increasing attention as a technology for achieving small, lightweight, low power consumption, and high-performance electronics. The MEMS is a system where minute mechanical elements and electronic circuit elements are integrated using silicon process technology.
An example structure of electrostatic type actuators using MEMS technology has been disclosed in U.S. Pat. No. 5,578,976. In order to bring an electrostatic actuator into a closed state (where the upper electrode and the lower electrode come in contact with each other via a insulating film, a potential difference is applied between the upper electrode and the lower electrode so that such electrostatic attraction is provided between the electrodes that is greater than the elastic force of a movable unit to which the upper electrode is fixed.
For the electrostatic actuator in its closed state, the upper electrode and the lower electrode come in contact with each other via the insulating film and larger capacitance is provided between the upper electrode and the lower electrode than in the opened state. At this moment, charges can be injected and trapped into the insulating film using the FN tunnel or Poole-Frenkel mechanism. This phenomenon is expressed as dielectric charging in electrostatic type actuators.
When the amount of charges trapped into the insulating film due to the dielectric charging becomes larger than a certain value, the upper electrode is attracted toward the charges in the insulating film. Accordingly, the electrostatic actuator cannot be changed from its closed state to opened state even if the potential difference between the upper electrode and the lower electrode is set to 0V. This phenomenon is expressed as stiction due to dielectric charging. One of means for avoiding such stiction has been described in, e.g., G. M. Rebeiz, “RF MEMS Theory, Design, and Technology,” Wiley-Interscience, 2003, pp. 190-191. It is difficult, however, to eliminate charges trapped into the insulating film and completely exclude stiction. Therefore, there is a need for a semiconductor device that may determine the states of an electrostatic actuator in a simple and accurate way, including whether or not stiction occurs.